This project is designed to investigate the size and spatial distribution of cortical neuron "colonies" in the primate motor cortex that are associated with individual muscles or closely related groups of muscles, as well as the activity of neurons in such colonies during defined voluntary motor behaviors. Intracortical microstimulation (ICMS) is used to map regions that produce excitation or inhibition of particular muscles or muscle groups, and the resultant cortical maps are compared with these for synergist or antagonist muscle groups. Cortical cell discharge patterns during normal movements are evaluated with respect to the excitation or inhibition of muscle activity that is produced by ICMS. Intracortical capacitor stimulating electrodes are being evaluated for efficacy, stability and safety for chronic implantation.